Previously proposed such heat exchange equipment is disclosed in U.S. Pat. No. 5,771,699. This discloses an air conditioning system which employs reverse cycle refrigeration apparatus to condition air inside a building for heating in the winter months, and for cooling in the summer months, utilizing one heat exchanger coil disposed in heat exchange relation to the flow of conditioned air circulating within a building, and two heat exchanger coils disposed in heat exchange relation to the flow of ambient air circulating outside a building, wherein each heat exchanger coil comprises a separate and singular component part of a single air conditioning circuit connected to, and served by one single compressor; and wherein each of the outside heat exchanger coils are designed to change functions independently of the other, from that of an evaporator, to that of a condenser, for the purpose of inhibiting the accumulation of frost on, and/or removing frost from the outside heat exchanger coil when the heat pump is operating in the heating mode without reversing the flow of refrigerant within, or impeding the flow of refrigerant to the inside heat exchanger coil, whereby the inside heat exchanger coil will continue to function in the condenser mode, and will continue to furnish heat to the inside of a building during the defrost cycle of either of the said outside heat exchanger coils, and whereby heat generated by one said outside heat exchanger coil during the defrost cycle of that coil will be reabsorbed into the heat pump system via the other outside heat exchanger coil and circulated through the same refrigeration circuit, in a manner that will improve the efficiency of the heat pump.
Previously proposed equipment provides respective thermostatic control means for the outside coils. Furthermore, it is possible that both coils may require defrosting simultaneously.